Laboratory investigation on the use of recycled materials in bituminous mixtures for dense-graded wearing course

Reduce, recycle and reuse of materials are the three crucial procedures that affect the economy of the current century, which are mandatory in preserving and protecting the planet for the next generations. In this field, the construction of road pavements plays fundamental role since huge amount of materials are involved, particularly the bituminous mixtures. This is the reason why the efforts of the scientific community were, and still are, addressed to investigate alternative pavement solutions in which recycled and reused materials, which mostly come from end-of-life pavement removal, can be included with the goal of reducing landfill operations. Moreover, a lot of these efforts were directed to reuse of recycled materials in producing bituminous mixtures for structural pavement layers, and not to the wearing course. Therefore, in order to be a step ahead of the current technical and scientific approaches, this research focused on the study of the effects of the concurrent use of reclaimed asphalt (RA), stabilized bottom ashes (SBA) from urban waste incinerators, and waste engine oil (WEO) in substitution of commercial rejuvenators. Moreover, the benefits deriving from the use of polymer additives were assessed. In this regard, a set of compaction, volumetric and mechanical tests were performed at laboratory scale, demonstrating that it is possible to use high amounts of RA (20 % and 60 %) in bituminous mixtures for wearing courses, also combined with SBAs and WEO. More in detail, the obtained results demonstrate that: both RA and SBAs generally increase mixtures’ stiffness (as confirmed by stiffness Master Curves and Indirect Tensile Strength results); SBA can be used as artificial aggregates; and WEO is able to act as fluxing agent to obtain mixture’s viscosity reduction.